i About this experiment — click to learn the physics ▼
What you're looking at
This is an electrostatics sandbox. You drop point charges — protons (+) and electrons (−) — onto the field and the simulation draws the electric field they create together, plus the net force each charge feels from all the others. Click to add charges, drag them around, and watch the whole picture update.
Coulomb's law
Any two charges exert a force on each other along the line joining them. Like charges repel, opposite charges attract, and the strength falls off as the square of the distance:
When several charges are present, the force on any one of them is just the vector sum of the forces from every other charge — the principle of superposition. The gold arrows show that net force; a longer arrow means a stronger pull or push.
The electric field
Rather than track forces between every pair, we describe the field each charge sets up in the space around it. The field at a point is the force a tiny positive test charge would feel there, and fields add by superposition too:
Reading the field lines
- Lines start on positive charges and end on negative charges (or run off to infinity).
- The arrow on a line shows the direction a + charge would be pushed.
- Density matters: where lines bunch together the field is strong; where they spread out it's weak. More lines sprout from a bigger charge — try raising the magnitude.
- Field lines never cross, because the field points one definite way at each point.
Things to try
Load the Dipole preset to see the classic + / − pattern. Place two like charges and notice the field pushed into the empty midpoint between them. Build a row of + charges to approximate a charged plate and see the field become uniform between them.